1. Field of the Invention
The invention relates to a printing device comprising a circular cylindrical anvil which is rotatable about its longitudinal axis, and a printing head which is displaceable along a guide rod parallel to the longitudinal axis of the anvil, being arranged opposite the said anvil and coupled to a displaceable distance roller which is spring-biased against the anvil and which is rotatable about a shaft which is parallel to the longitudinal axis of the anvil, the printing heat being displaced in a direction perpendicular to the longitudinal axis of the anvil by movement of the distance roller with respect to the anvil.
The invention is preferably applied in printing devices for printing characters which are composed of dot-like or line-like elements and which are produced by exerting pressure and/or impact on a record carrier. The use of the invention, however generally is advantageous for all printing devices in which a constant distance is required between the printing members and the record carrier, such as in printing devices in which alternately record carriers of varying thickness or a plurality of record carriers must be simultaneously printed. The invention is also applicable to printing devices in which the same type of record carrier is always used, because thickness variations in the record carrier itself could cause a variation of the distance between the printing members and the record carriers during printing.
2. Description of the Prior Art
In known printing device (German Patent Application No. 2,248,262 and U.S. Pat. No. 3,750,792) a so-called sensor which is spring-biased against the record carrier is used for maintaining a constant distance between the printing head and the record carrier. This sensor may be constructed as a rotatable roller (German Patent Application No. 2,248,262), or a non-rotatable sensor which slides over the record carrier (U.S. Pat. No. 3,750,792). In both known devices, however, the sensor is coupled to a printing head which is displaceable in a direction perpendicular to the longitudinal axis of the anvil and which accommodates the printing members. The printing head is arranged on a carriage which itself is movable in a direction parallel to the longitudinal axis of the anvil.
Such known devices have the drawback that a comparatively large mass must be quickly displaced in a direction parallel to the longitudinal axis of the anvil, because a transverse guide for the printing head separation distance must be provided on the carriage. This imposes restrictions as regards the printing speed, notably for printing devices comprising an intermittently tently moving carriage.